The present invention, in some embodiments thereof, relates to inkjet printing techniques and, more particularly, but not exclusively, to improved processes and compositions for inkjet printing of high resolution color images on stretchable and/or flexible absorptive and non-absorptive substrates of all colors.
The ever growing market of printing complex designs and images on almost every type of surface, and especially on knitted, woven and non-woven textile surfaces, plasticized and laminated fabrics (soft signage) and the likes, creates demands for new and more versatile printing technologies and materials. One such demand is for ink compositions and technologies which will be suitable for printing long lasting, durable, abrasion resistant, water-, detergent- and chemical-fast color images on a variety of materials, which will not wear out rapidly upon use, handling, washing and exposure to the environment. The garment industry is possibly the most demanding in terms of printing high quality and durable prints of textile, adding some requirements from the product, such as pleasant hand-feel of the printed area, flexible (bendable without cracking), stretchable and aerated print area, as well as following the guidelines of internationally accepted standards such as the Oeko-Tex Standard 100 (an international testing and certification system for textiles, limiting the use of certain chemicals, which was developed in 1992) and GOTS (Global Organic Textile Standard).
One of the most promising technologies for printing high quality color images, particularly in small batches of varying contents (short runs of variable data), on a wide variety of types and shapes of substrates, such as textile surfaces, is inkjet printing. Inkjet printing is a wide-spread technique in which a stream of a specific liquid ink composition is ejected as droplets from a cluster of minute nozzles (printheads) in response to electrical signals generated by a microprocessor to record characters and patterns on the surface of a printing subject without making direct contact between the ink application apparatus and the surface of the subject (non-impact printing). A typical inkjet printing system includes methods and apparatus in which electric signals are converted to mechanical signals for a continuous or on-demand jetting of an ink composition which is continuously supplied and stored in a nozzle head portion, to thereby record characters, symbols and patterns on the surface of a subject.
Reviews of various aspects of inkjet printing can be found in publications such as Kuhn et al., Scientific American, April, 1979, 162-178; Keeling, Phys. Technol., 12(5), 196-203 (1981); U.S. Pat. Nos. 3,060,429, 3,298,030, 3,373,437, 3,416,153, 3,673,601, 4,312,007 and 4,380,770; and numerous other publications.
The presently available ink compositions, including compositions that are suitable for inkjet printing, include aqueous-based ink compositions and non-aqueous solvent-based ink compositions. The more commonly used inkjet compositions are aqueous-based ink compositions, which typically include water and a colorant, usually a dye or pigment dispersion, and may further contain a number of additives for imparting certain attributes to the ink as it is being applied (jetted), e.g., improved stability and flow, anti-corrosiveness, and feather and bleeding resistance), as well as attributes to affect its final cured properties such as the capability to form chemical bonds with the substrate, improved adhesion to the substrate, flexibility, stretchability, softness and the like.
One of the challenges in printing on fabric is its absorbability, which is far more challenging than that of, for example, paper or non-adsorbent substrates.
To ensure high quality images by inkjet, the ink composition should be characterized by free passage through the nozzles, minimal bleeding, paddling and/or smearing, uniform printing on the surface of the subject, wash-fastness, simple system cleaning and other chemical and physical characteristics. To meet these requirements, the ink composition should be characterized, for example, by suitable viscosity, solubility, volatility, surface tension, compatibility with other components of the printing system and, in cases of continuous flow inkjet printing, electrical resistance, and further be applied using suitable apparati, techniques and processes.
In case of printed fabrics (e.g., printed garments), in order to sustain wear and tear due to frequent use and wash cycles, the printed image on the final product, as well as the final product itself, should exhibit the properties of an elastic yet aerated film, and therefore the ink composition should also contain components which can impart such compressibility (softness), plasticity, elasticity, flexibility and stretchability.
During the last decades, numerous techniques, compositions and apparati for inkjet printing in general, and particularly on textile and garments, have been developed. See, for example, U.S. Patent Application Nos. 2002/0022120, 2002/0060728, 2003/0142167, 2003/0157304 and 2005/0098054 and U.S. Pat. Nos. 4,702,742, 5,349,021, 5,594,044, 5,645,888, 5,988,791, 6,042,228, 6,117,921, 6,126,281, 6,140,391, 6,322,620, 6,326,419, 6,341,856, 6,513,924, 6,536,894, 6,606,427, 6,626,530 and 6,879,378.
U.S. Pat. Nos. 6,196,674 and 6,500,880 and U.S. Patent Application Nos. 20010008908 and 20010018472 teach inkjet compositions which are said to alleviate feathering and bleeding problems of inkjet printing on semi-absorptive substrates, mainly paper and stationeries which are not designed or expected to bend or stretch.
Typically the thickness and the absorbance in the vertical direction (depth), as oppose to its surface in the XY field or horizontal direction, of any untreated fabric, are many orders of magnitude higher as that of paper, and particularly when compared to inkjet paper media, which is pre-treated to exhibit specific ink-retention and absorption properties. While contemporary inkjet paper media is designed for inkjet print and therefore supplied after being pretreated to retain the liquid inkjet, for example, by coating the surface of the paper with fumed silica and alike. Typical textile pieces are not intended for digital print application and therefore must be either pretreated “off-line” prior to the printing process.
IL Patent No. 162231 and WO 2005/115089 by the present assignee, which are hereby incorporated by reference as if fully set forth herein, teach processes and systems for printing high quality, high resolution, multi-color images on fibrous or porous materials or other ink absorbing materials, or on materials having high surface tension with the ink liquid, and especially over garments, effected by applying a wetting composition prior to applying an ink composition and formation of the images. Specifically, the process of printing an image on a surface is effected by contacting at least a part of the surface, preferably covering slightly more than the area which is intended for the image, with a wetting composition so as to wet that part of the surface. The wetting composition is capable of interfering with the engagement of a liquid ink composition with material, such that when applying the liquid ink composition on the wetted surface, the ink is kept from smearing and absorbing in the material, allowing to form a high-quality image on the wet part of the absorptive surface. According to some embodiments disclosed in IL Patent No. 162231 and WO 2005/115089, the wetting solution is applied in a way so as to soak the textile media therewith.
IL Patent No. 162231, WO 2005/115089 and U.S. Patent Application Nos. 20070103528 and 20070104899, by present assignee, therefore teach methodologies involving pre-treatment of textile pieces which are wetted “on the fly”.
U.S. Pat. No. 7,134,749 by the present assignee, which is hereby incorporated by reference as if fully set forth herein, teaches a method and apparatus for color printing on a dark textile piece. According to the teachings of this patent, the method includes the steps of digitally applying a white opaque ink layer directly onto a dark textile piece, and digitally printing a colored image on the white ink layer. Specifically, the method for color printing on a dark textile piece is effected by digitally printing, by means of an inkjet printing head, an opaque white ink layer directly onto a dark textile piece; and digitally printing a colored image on the white ink layer. The digital printing of the white ink layer is performed such that the white ink layer substantially covers, without exceeding, the designed area of the colored image, and further such that the white ink layer and the colored image are substantially coextensive.
U.S. Patent Application Nos. 20070103528 and 20070104899, by the present assignee, which are hereby incorporated by reference as if fully set forth herein, teach individual and integrated processes, methods and compositions for printing high quality, high resolution, multi-color images on lightly and/or darkly colored fibrous or porous materials or other ink absorbing materials, which also provide a mechanism for drop immobilization aimed at inhibiting the adsorption by fabric, the bleeding, smearing, paddling and feathering of the jetted ink droplets. These integrated processes are effected by digitally printing a layer of an opaque, lightly colored ink composition, followed by digitally printing the colored image thereon, and optionally further involve applying a wetting composition prior to and/or subsequent to printing of these layers. These documents further provide multi-component compositions and processes utilizing wetting compositions and/or two-part liquid ink compositions which can interact therebetween as property-adjusting and property-sensitive pairs, so as to effect a chemical and/or physical change in one or more of these parts, and thus obtain improved binding and color perception of the resulting images on surfaces, particularly in cases of absorptive substrates.